Legal Pot Is a Public Health Menace

Public opinion is moving in favor of marijuana, even as medical research raises fresh alarms.

The great irony, or misfortune, of the national debate over marijuana is that while almost all the science and research is going in one direction—pointing out the dangers of marijuana use—public opinion seems to be going in favor of broad legalization.

For example, last week a new study in the journal Current Addiction Reports found that regular pot use (defined as once a week) among teenagers and young adults led to cognitive decline, poor attention and memory, and decreased IQ. On Aug. 9, the American Psychological Association reported that at its annual convention the ramifications of marijuana legalization was much discussed, with Krista Lisdahl, director of the imaging and neuropsychology lab at the University of Wisconsin-Milwaukee, saying: “It needs to be emphasized that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neurocognitive damage, especially in youth.”

Since few marijuana users limit themselves to use once a week, the actual harm is much worse for developing brains. The APA noted that young people who become addicted to marijuana lose an average of six IQ points by adulthood. A long line of studies have found similar results—in 2012, a decades-long study of more than 1,000 New Zealanders who frequently smoked pot in adolescence pegged the IQ loss at eight points.

Yet in recent weeks and months, much media coverage of the marijuana issue has either tacitly or explicitly supported legalization. A CCN/ORC International survey in January found that a record 55% of Americans support marijuana legalization.

The disconnect between science and public opinion is so great that in a March WSJ/NBC News poll, Americans ranked sugar as more harmful than marijuana. The misinformation campaign appears to be succeeding.

Here’s the truth. The marijuana of today is simply not the same drug it was in the 1960s, ’70s, or ’80s, much less the 1930s. It is often at least five times stronger, with the levels of the psychoactive ingredient tetrahydrocannabinol, or THC, averaging about 15% in the marijuana at dispensaries found in the states that have legalized pot for “medicinal” or, in the case of Colorado, recreational use. Often the THC level is 20% or higher.

With increased THC levels come increased health risks. Since Colorado legalized recreational use earlier this year, two deaths in the state have already been linked to marijuana. In both cases it was consumed in edible form, which can result in the user taking in even more THC than when smoking pot. “One man jumped to his death after consuming a large amount of marijuana contained in a cookie,” the Associated Press reported in April, “and in the other case, a man allegedly shot and killed his wife after eating marijuana candy.” Reports are coming out of Colorado in what amounts to a parade of horribles from more intoxicated driving to more emergency hospital admissions due to marijuana exposure and overdose.

Over the past 10 years, study after study has shown the damaging effect of marijuana on the teenage brain. Northwestern School of Medicine researchers reported in the Schizophrenia Bulletin in December that teens who smoked marijuana daily for about three years showed abnormal brain-structure changes. Marijuana use has clearly been linked to teen psychosis as well as decreases in IQ and permanent brain damage.

The response of those who support legalization: Teenagers can be kept away from marijuana. Yet given the dismal record regarding age-restricted use of tobacco and alcohol, success with barring teens from using legalized marijuana would be a first.

The reason such a large number of teens use alcohol and tobacco is precisely because those are legal products. The reason more are now using marijuana is because of its changing legal status—from something that was dangerous and forbidden to a product that is now considered “medicinal,” and in the states of Colorado and Washington recreational. Until recently, the illegality of marijuana, and the stigma of lawbreaking, had kept its use below that of tobacco and alcohol.

Legality is the mother of availability, and availability, as former Health, Education and Welfare Secretary Joseph A. Califano Jr. put it in his 2008 book on substance abuse, “High Society,” is the mother of use. According to the Substance Abuse and Mental Health Services Administration, currently 2.7 million Americans age 12 and older meet the clinical criteria for marijuana dependence, or addiction.

Mark A.R. Kleiman, a professor of public policy at the University of California, Los Angeles, has estimated that legalization can be expected to increase marijuana consumption by four to six times. Today’s 2.7 million marijuana dependents (addicts) would thus expand to as many as 16.2 million with nationwide legalization. That should alarm any parent, teacher or policy maker.

There are two conversations about marijuana taking place in this country: One, we fear, is based on an obsolete perception of marijuana as a relatively harmless, low-THC product. The other takes seriously the science of the new marijuana and its effect on teens, whose adulthood will be marred by the irreversible damage to their brains when young.

Supporters of marijuana legalization insist that times are changing and policy should too. But they are the ones stuck in the past—and charting a dangerous future for too many Americans.

Mr. Bennett is a former secretary of education (1985-88) and was the first director of the National Drug Control Policy (1989-90). Mr. White is an attorney in Princeton, N.J.